The present invention relates to an electro-photographic photoreceptor which contains a novel hydrazone or styryl compound.
Hitherto, inorganic photoconductive substances such as selenium, cadmium sulfide, zinc oxide and silicon have been known for photoreceptors of electrophotographic system and widely studied and have been put to practical use. Recently, organic photoconductive materials have also been intensively studied as electrophotographic photoreceptors and some of them have been practically used.
In general, inorganic materials are unsatisfactory, for example, selenium photoreceptors have problems such as low heat stability, deterioration of characteristics due to crystallization and difficulty in production and cadmium sulfide photoreceptors have problems in moisture resistance, endurance and disposal of industrial waste. On the other hand, organic materials have advantages such as good film-formability, excellent flexibility, light weight, high transparency and easy designing of photoreceptors for wavelength of wide region by suitable sensitization. Thus, organic materials have increasingly attracted public attention.
Photoreceptors used in electrophotographic process are required to possess the following fundamental properties, namely, (1) high chargeability for corona discharge in the dark place, (2) less leakage of the resulting charge in the dark place (dark decay), (3) rapid release of charge by irradiation with light (light decay), and (4) less residual charge after irradiation with light.
Extensive research has been made on photoconductive polymers as organic photoconductive substances including polyvinylcarbazole and others, but these are not necessarily sufficient in film-formability, flexibility and adhesion and besides these cannot be said to have sufficiently possess the above-mentioned fundamental properties as photoreceptor.
On the other hand, in case of organic low molecular photoconductive compounds, photoreceptors excellent in film-formability, adhesion, flexibility and other mechanical strengths can be obtained therefrom by selection of binders, etc. used for production of photoreceptors, but it is difficult to find compounds suitable to keep the characteristic of high sensitivity.
In order to improve these problems, there has been made development of organic photoreceptors having higher sensitivity by bearing the carrier generating function and the carrier transporting function by different substances. Characteristics of such photoreceptor called double-layered structure is that materials suitable for respective functions can be selected from wide variety of materials and photoreceptors having optional performances can be easily produced and thus intensive research has been made on such photoreceptors.
As explained above, many improvements have been made in production of electrophotographic photoreceptors, but those which meet the requirements for fundamental properties mentioned above and high endurance have not yet been obtained.